Section 9: "Randomized Evaluations" from Heckman, J. and Vytlacil, E. (2007). "Econometric Evaluation of Social Programs, Part II: Using the Marginal Treatment Effect to Organize Alternative Economic Estimators to Evaluate Social Programs and to Forecast Their Effects in New Environments," in J. Heckman and E. Leamer, eds. Handbook of Econometrics, Vol. 6. Amsterdam: North-Holland.